No Relationship Between Population Size and Per Capita Income

I had always been curious about this, thinking that perhaps there would be a positive correlation; being part of a big country opens up a big market to you, and (one might reason) if a population can function as a large unified country, that means that somehow, culture and institutions are functioning well and this will affect economics. But this is not the case. There was no relationship between population and per capita income, which also implies that over time there is no relationship between population and growth rate.

Of course there are population outliers, but even after I took out all the countries with populations of over 100 million (there are 12) no relationship appeared. In any event, from a policy-making standpoint, it's not clear what this would've meant anyway. (Quick! Join together with bigger countries so we'll get higher GDP!)

There has been work done on population growth rate (below, source), showing a negative relationship; interesting but not surprising, likely relating to demographic transition. Additionally, one of the effects of being in a country is that of the same currency across the population, so a separate question would be whether monetary union regions grow faster than non-union regions, but there are far fewer data points there.